The clinical syndrome of Osteoarthritis, which is also known as degenerative arthritis or degenerative joint disease, is characterized by loss of articular cartilage on adjacent bony surfaces resulting in discomfort, loss of motion, and functional impairment. In a similar fashion, inflammatory arthritis, for example, rheumatoid arthritis, results in loss of cartilage surfaces from both biochemical and mechanical means. As the bony surfaces become less protected by cartilage, the patient experiences pain, motion limitation, potential joint instability, and eventual functional loss.
Interphalangeal joint arthritis is the development of Osteoarthritis at a patient's finger joint, for example, the proximal interphalangeal (PIP) joint, i.e. PIP joint arthritis. The PIP joint of the hand is defined by the coupling of the proximal phalanx bone and the middle phalanx bone. Metacarpophalangeal (MCP) joint arthritis is characterized by the development of changes consistent with articular cartilage destruction at the joint between the metacarpal bone and the proximal phalanx bone.
Treatment options for PIP joint and MCP joint arthritis include, for example, splints, i.e. temporary immobilization of the patient's articulating joints, medication, corticosteroid injections, and surgery. Surgical treatments may be generally characterized as “motion-sparing” and “motion-eliminating”. Motion-sparing treatments may include, for example, implantation of articulating devices (arthroplasties), and motion-eliminating may include, for example, joint fusion treatments (arthrodesis). For PIP joint arthritis, adjacent portions of the proximal and middle phalanx bones may be replaced. The same is true for the MCP joint, i.e. replacing adjacent portions of the metacarpal and proximal phalanx bones. In both cases, the mobility of the joints is maintained by implantation of biologic or artificial materials that permit the joint to move through an arc of motion, while attempting to relieve pain.
An approach to a motion sparing PIP joint implant is disclosed in U.S. Pat. No. 6,699,292 to Ogilvie et al. The PIP joint implant includes first and second portions, each having mating heads. The mating heads provide a PIP joint prosthesis that may allow smooth articulation.
Another approach to a motion sparing distal interphalangeal (DIP) joint implant is disclosed in U.S. Pat. No. 6,475,242 to Bramlet. The implant includes a pair of screws for securing to the middle and distal phalanges. The implant further includes a flexible connector coupled to the heads of each screw. The flexible connector may comprise a U-shaped bow or a mechanical joint.
A typical approach to motion-eliminating PIP joint or MCP joint arthrodesis includes the tension band method, i.e. simple pinning with a smooth wire or plating with conventional implants. These methods include potential drawbacks, for example, technically-demanding implantation procedure resulting in less than optimum accuracy, potential for subsequent hardware removal due to smooth wire migration or tension band “knot” irritation/abrasion on local tendons, and nonunion (or failure of the two bones to unite at the site of the desired fusion).